Structural and electronic properties of electron cyclotron resonance plasma deposited hydrogenated amorphous carbon and carbon nitride films

摘要

Hydrogenated amorphous carbon and carbon nitride films (a-C_(1-x)N_(x):H) have been synthesized from methane, acetylene, or acetylene-nitrogen precursor gases using a high density electron cyclotron resonance plasma. The deposition and etching rates, along with the film stoichiometry, density, Raman signature of the sp~(2) phase, and optical and transport properties, have been studied as a function of plasma parameters (microwave power and negative bias of the substrate). While low-density H-rich carbon films have been grown from methane for ion energies up to 200 eV, films grown using acetylene have been obtained at high deposition rate (1.1 nm s~(-1)) with H content below 25 H at. and density of 2.0 g cm~(-3), which makes them interesting as electronic materials. For dense carbon nitride alloys, the maximum (N/N+C)=0.35 is limited by the vanishing growth rate, which results from ion-assisted chemical etching mechanisms. A larger N_(2) plasma etching rate related with lower film density is observed for (N/N+C) values above 0.20. As a function of the N content, Raman spectra give evidence of a continuous structural ordering of the sp~(2) phase, which is confirmed by a modeling of the ohmic conductivity σ(T) data based on hopping transport within a bandtail distribution of localized π states. With increasing N content, a better overlap of p orbitals along with an increase in the localization length are expected as a consequence of a less constrained environment. A maximum of the room-temperature conductivity at (N/N+C)=0.28 reveals the onset of a transition towards polymeric alloys with lower mean coordination number.